The invention relates to a switch with a digital display, and more particularly, to such a switch may be used as input means for supplying reference information to a digital circuit such as a digital controller, a microcomputer or the like.
A variety of switches including rotary switches, and pushbutton switches are used for inputting numerical reference information into a digital circuit. For example, a thumbwheel switch is known as one form of a rotary switch, and includes a thumbwheel having decimal numbers "0" to "9" borne thereon. By turning the thumbwheel so that one of the numbers is selectively brought to a home position where the number is displayed, a corresponding decimal digit is supplied as an input from the switch at the same time as it is displayed. A plurality of such thumbwheel switches may be combined to supply a multi-digit decimal number as an input and also to display such number.
However, where a plurality of such thumbwheel switches are used in combination to input and display a multi-digit decimal number, it will be understood that unnecessary number or numbers may be temporarily displayed and inputted when simultaneously changing the multiple digits to another desired sequence. By way of example, when switching the display of a two-digit number from "19" to "20", the switching operation which takes place for each digit causes unnecessary numbers such as "10" or "29" to be temporarily displayed and inputted in the course of such operation.
To overcome such an inconvenience, a read circuit is provided which, instead of instantly reading the numerical value indicated by the thumbwheel switches, is responsive to the operation of an input enable switch, which is actuated after the completion of operating the thumbwheel switches, so that the desired new value can be read unambiguously. However, it will be appreciated that such an arrangement results in a complication of the switching mechanism and the read circuit as well as a troublesome operation on the part of an operator.
On the other hand, when a pushbutton switch arrangement which is used in a table-top electronic calculator is used as means for inputting numeral reference information, an inconvenience results when the power supply is interrupted such that information is lost which indicates which button or buttons have been depressed.
If it is desired to prevent such an inconvenience, it is necessary to provide a separate charging unit which is normally maintained charged so that in the event a power supply is interrupted, it feeds a storage element or elements to prevent the loss of information stored therein. Alternatively, a non-volatile memory such as EAROM (electrically alterable read only memory) may be provided to store numerical information therein before the power supply is interrupted. However, the provision of a charging unit or non-volatile memory also results in a complication of the switching arrangement and the read circuit. In addition, the use of a non-volatile memory requires a troublesome switch operation in that numerical information must be inputted into the memory before the power supply is interrupted.
From the foregoing discussions, it will be appreciated that the use of conventional means which involves thumbwheel switches or pushbutton switches is not adequate for use as means for inputting numerical reference information into a digital circuit such as a digital controller, digital computer or the like, which require an accurate and rapid inputting of numerical reference information, and which must maintain the condition of switches which they assumed before the interruption of the power supply.